Pigments that are used in polar environments must be readily dispersible and must be hydrophilic. Among the most important pigments are those comprised of a transition metal or an oxide or complex thereof. Accordingly, it is important for certain applications to be able to render hydrophilic or to increase the hydrophilicity of the surface of such transition metal-containing pigment particles.
Treatments to render iron-containing materials hydrophobic are known and are used to render the iron-containing pigments suitable for use in many ink applications; however, most of the applications for iron-containing materials, especially iron oxide, are hydrophilic (as in paint). Though the surface of most iron-containing materials inherently is hydrophilic in nature, a further increase in surface hydrophilicity will lead to more compatibility with the polar vehicle systems used in various applications.
Thus, a need exists for a fast and economical way to render hydrophilic or to increase the hydrophilicity of the surface of transition metal-containing pigment particles, so that such particles can be easily dispersed in a wide variety of solvents or vehicle systems. Such a need is met by the method of the present invention.